VSE: Add "Mirror" menu to preview strip menu

This PR adds a "Mirror" menu to the Strip menu within the VSE preview.
This menu is similar to the "Mirror" menu in the view3d "Object" menu.
It allows the user to access the mirror operator through a menu, rather
than via a shortcut.

Pull Request: https://projects.blender.org/blender/blender/pulls/142506

scripts/startup/bl_ui/space_sequencer.py

@@ -9,6 +9,7 @@ from bpy.types import (
     Panel,
 )
 from bpy.app.translations import (
+    pgettext_iface as iface_,
     contexts as i18n_contexts,
     pgettext_iface as iface_,
     pgettext_rpt as rpt_,
@@ -994,6 +995,31 @@ class SEQUENCER_MT_strip_animation(Menu):
         layout.operator("anim.keyframe_clear_vse", text="Clear Keyframes...")
 
 
+class SEQUENCER_MT_strip_mirror(Menu):
+    bl_label = "Mirror"
+
+    def draw(self, _context):
+        layout = self.layout
+        layout.operator_context = 'INVOKE_REGION_PREVIEW'
+
+        layout.operator("transform.mirror", text="Interactive Mirror")
+
+        layout.separator()
+
+        for (space_name, space_id) in (("Global", 'GLOBAL'), ("Local", 'LOCAL')):
+            for axis_index, axis_name in enumerate("XY"):
+                props = layout.operator(
+                    "transform.mirror",
+                    text="{:s} {:s}".format(axis_name, iface_(space_name)),
+                    translate=False,
+                )
+                props.constraint_axis[axis_index] = True
+                props.orient_type = space_id
+
+            if space_id == 'GLOBAL':
+                layout.separator()
+
+
 class SEQUENCER_MT_strip_input(Menu):
     bl_label = "Inputs"
 
@@ -1147,6 +1173,7 @@ class SEQUENCER_MT_strip(Menu):
         strip = context.active_strip
 
         if has_preview:
+            layout.menu("SEQUENCER_MT_strip_mirror")
             layout.separator()
             layout.operator("sequencer.preview_duplicate_move", text="Duplicate")
             layout.operator("sequencer.copy", text="Copy")
@@ -3202,6 +3229,7 @@ classes = (
     SEQUENCER_MT_strip_text,
     SEQUENCER_MT_strip_show_hide,
     SEQUENCER_MT_strip_animation,
+    SEQUENCER_MT_strip_mirror,
     SEQUENCER_MT_strip_input,
     SEQUENCER_MT_strip_lock_mute,
     SEQUENCER_MT_image,